The present invention relates to an ion-trap mass analyzing apparatus and its analyzing method, particularly to an ion-trap mass analyzing apparatus and its analyzing method preferred to analyze the mass of an ion at a high velocity and a high resolution.
An ion trap mass analyzing apparatus is an apparatus for analyzing the mass by trapping ions in a trap field, ejecting the trapped ions from the trap field by various methods, and detecting the ions. Because the ion-trap mass analyzing apparatus traps and detects ions, it realizes a high-sensitivity numerical analysis and, therefore, it has been widely developed in recent years. To eject ions from an ion trap field, it is general to use the so-called auxiliary electric field. Energy is supplied to ions by the auxiliary electric field to increase the amplitude of the ions, thereby ejecting the ions from the trap field. Many types of auxiliary electric fields are also proposed. For example, a dipole auxiliary AC electric field and a quadrupole auxiliary AC electric field are listed.
A dipole auxiliary electric field provides an electric field almost not depending on the position coordinates of an ion as disclosed in the official gazette of Japanese Patent Laid-Open No. 103856/1990. Therefore, when the amplitude and the velocity of an ion oscillation increase, the resistance force to ions due to collision with batter gas increases by a value equivalent to the increase of the amplitude and the velocity, and spatial dispersion between ions contracts. Thus, because the auxiliary electric field has a function of decreasing degree of dispersion in the position coordinates, the ejection time difference of ions decreases and the resolution is improved. However, because the amplitude of ion oscillation increase with the constant velocity, the auxiliary field has also disadvantages that emission of ions requires a lot of time and the scanning rate of mass numerical analysis cannot be increased.
However, the quadrupole auxiliary AC electric field supplies an electric field depending on the position coordinates of an ion as disclosed in U.S. Pat. No. 3065640. Therefore, when the amplitude and the velocity of an ion oscillation increase, the increasing amount of amplitude of ion oscillation further increases by a value equivalent to the increase of the amplitude of the ion is oscillation. Therefore, as the amplitude of the ion oscillation increases, the increasing amount of amplitude increases, ions are more quickly emitted, thereby accelerating the scanning of mass numerical analysis. However, because the electric field depends on the position coordinates of an ion, the difference of the ejection time of each ion increases.